SINGAPORE (Reuters) - Staples such as cassava on which millions of people depend become more toxic and produce much smaller yields in a world with higher carbon dioxide levels and more drought, Australian scientists say.

The findings, presented on Monday at a conference in Glasgow, Scotland, underscored the need to develop climate-change-resistant cultivars to feed rapidly growing human populations, said Ros Gleadow of the Monash University in Melbourne.

Gleadow's team tested cassava and sorghum under a series of climate change scenarios, with particular focus on different CO2 levels, to study the effect on plant nutritional quality and yield.

Both species belong to a group of plants that produce chemicals called cyanogenic glycosides, which break down to release poisonous cyanide gas if the leaves are crushed or chewed.

Around 10 percent of all plants and 60 percent of crop species produce cyanogenic glycosides.

The team grew cassava and sorghum at three different levels of CO2; just below today's current levels at about 360 parts per million in the atmosphere, at about 550 ppm and about double at 710 pm.

Current levels in the air are just under 390 ppm, around the highest in at least 800,000 years and up by about a third since the start of the Industrial Revolution.

"What we found was the amount of cyanide relative to the amount of protein increases," Gleadow told Reuters from Glasgow, referring to cassava. …